96 Queries arid Arisivers. 



That I have always considered uniformity in the manner in which observ- 

 ations should be made by meteorologists, not only with respect to time, but 

 as regards instruments of similar construction, of the greatest importance, 

 I need only refer to a letter written by me, in February, 1823 (see Monthly/ 

 Magazine, vol. Iv. p. 207.), recommending the establishment of a Meteorolo- 

 gical Society in the metropolis ; and I should be most happy, at any time, to 

 assist in the arrangement of some plan by which that desirable object could 

 be obtained. 



I will now proceed, without further preface, to state the method practised 

 by me in making my observations. The thermometer and barometer are 

 examined every day at 8 a. m., 3 p. m. (esteemed the hottest period of the 

 day), and 10 p. m., and the extreme of cold is ascertained by a self-register- 

 ing thermometer; thus giving four observations of that instrument, all of 

 which are duly registered, and the monthly mean is found by dividing the sum 

 of all these by the number of observations, which, of course, varies with the 

 number of days in each month. The rain and evaporation are measured 

 every morning at 8 o'clock, and the wind reported, if the prevailing wind of 

 the day. From this statement, Mr. Gorrie will see that " I refer to the 

 daily extremes^ The annual mean results from the division of the sum of 

 the monthly means by 12, or is the mean of means. If the averages of the 

 monthly extremes had been alone attended to, the annual mean for the last 

 year would have been lower than even that recorded in my report, being 

 only 47-6041. 



I subjoin the annual temperature for the last seven years, by which the 

 similitude between the years 1826 and 1828, noticed by Mr. Gorrie, very 

 evidently appears. It would be extremely gratifying to me, and, no doubt, 

 equally to your other meteorological readers, if Mr. Gorrie would favour us 

 with the course pursued by him, in making his observations, and it might 

 prove conducive to the adoption of some regular plan of observation among 

 meteorologists, at any rate among those who correspond with the Magazine 

 of Natural History. 



Annual mean for 1822 46-51° 



1823 44-26 



1824 46-11 



1825 46-81 



1826 47-37 



1827 46-25 



1828 47-75 



I remain. Sir, &c. — James G. Tatem. Wycombe, May 21. 1829. 



Vision over the Sea. — Sir, It is stated (Vol. II. p. 470.) that a person, 

 under favourable circumstances, could see over the surface of the ocean to 

 the extent of 150 miles. I would ask under what circumstances an object 

 on the surface of the earth or sea would be visible at that distance ; as, from 

 the convex form of the earth, it would require an elevation of nearly three 

 miles to bring it to a level with the horizon, or within the line of vision^ 

 setting aside the aid of refraction. Perhaps the limit of vision is unknown, 

 the distance at which a body may be seen appearing to depend upon its 

 size, the intensity of its light, and the state of the medium through which 

 the rays pass from it to the eye ; as the planets, though too remote for their 

 figure to be discerned by the unassisted eye, are yet conspicuous from the light 

 which they reflect ; whereas the fixed stars, from their immense distance, 

 would be totally invisible to us, if, like the planets, they shone only by re- 

 flected light. Perhaps some correspondent may furnish some useful inform- 

 ation on the subject, and oblige, among others, yoiu- obedient servant, — 

 T. E. Southwark, Dec. 4. 1829. 



